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Given a nested list of integers represented as a string, implement a parser to deserialize it.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Note:You may assume that the string is well-formed:

• String is non-empty.
• String does not contain white spaces.
• String contains only digits 0-9 , [ , - , , ] .

Example 1:

Given s = "324",

You should return a NestedInteger object which contains a single integer 324.

Example 2:

Given s = "[123,[456,[789]]]",

Return a NestedInteger object containing a nested list with 2 elements:

1. An integer containing value 123.
2. A nested list containing two elements:
    i.  An integer containing value 456.
    ii. A nested list with one element:
         a. An integer containing value 789.

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *     // Constructor initializes an empty nested list.
 *     public NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     public NestedInteger(int value);
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // Set this NestedInteger to hold a single integer.
 *     public void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     public void add(NestedInteger ni);
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
class Solution {
    int i = 1;
    public NestedInteger deserialize(String s) {

        if (s.charAt(0) != '[') return new NestedInteger(Integer.parseInt(s));

        NestedInteger ans = new NestedInteger();
        Integer num = null, k = 1;

        while (i < s.length()){
            char c = s.charAt(i++);

            switch(c){
                case '[':
                    ans.add(deserialize(s));
                    break;
                case ',':
                    if (num != null) ans.add(new NestedInteger(num * k));
                    num = null;
                    k = 1;
                    break;
                case ']':
                    if (num != null) ans.add(new NestedInteger(num * k));
                    return ans;
                default:
                    if (c == '-') k = -1;
                    else{
                        if (num == null) num = 0;
                        num = num * 10 + c - '0';    
                    }

            }
        }

        return ans;
    }
}